This PDF file contains the front matter associated with SPIE Proceedings Volume 9576 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The paper is understood as a continuation of a series of papers on surface metrology for application in quality control of printed matter. A stereoscopic device for extremely rugged applications, especially in quality control in printing industry, is presented. The device developed is based on variable tilted delay elements, which allow the use of a single imaging sensor and robust definition of parallax shift. Variable orthogonal delay elements were already used for variation of plane of focus in surface inspection, as described in previous papers. The method can be applied for macroscopical as well as for microscopic imaging. Beside mechanical design issues, the theoretical description, geometrical-optical approaches, and the treatment of the dispersion problem are discussed. Experimental results are included.

The flexible electronics market continues to grow at a rapid pace. Increasing numbers of applications employ the flexible components including displays, biomedical devices, smart apparel, and advanced sensors. To maintain performance and lifetime, many characteristics of the substrate and deposited layers must be monitored. This includes defects, surface roughness, and feature alignment. Ideally, in-situ metrology can be employed in roll-to-roll (R2R) equipment to allow for real-time process control. This presents the necessary three-dimensional metrology system with several challenging requirements: high vertical and transverse resolution, large field-of-view, extremely fast measurement times, and robust vibration immunity. This paper will discuss the design and performance of a compact, low-cost, large-field interferometric probe for in-situ measurement of R2R substrates. Samples with a variety of known and unknown features and roughnesses will be measured to characterize the performance of the system. Static and moving substrates will be measured to examine effects on results. Optimization of processing to allow for on-board analysis will be examined. Lastly, the paper will discuss how such probes may be arrayed to provide a high degree of areal coverage of the flexible substrate under test.

We describe a high accuracy frequency stepping method for a tunable diode laser to improve a three dimensional (3D) imaging approach based upon interferometric speckle imaging. The approach, modeled after Takeda, exploits tuning an illumination laser in frequency as speckle interferograms of the object (specklegrams) are acquired at each frequency in a Michelson interferometer. The resulting 3D hypercube of specklegrams encode spatial information in the x-y plane of each image with laser tuning arrayed along its z-axis. The specklegrams are processed by Fast Fourier Transformation (FFT) along the z-axis of the hypercube and the center of the peak in the resulting power spectrum for each pixel encodes its surface height. Alternatively, Takeda’s method can be followed which uses the phase of the FFT, unwraps it, and determines the surface height encoded in the slope of a line fitted to the phase. Wraparound of modulations above the Nyquist limit results in ambiguity in the optical path difference (OPD) between test and reference surfaces. Wraparound also amplifies measurement noise caused by errors and jitter in frequency stepping the illumination laser. By locking the laser frequency to successive cavity modes of a reference confocal interferometer, tuning is precisely controlled resulting in dramatically improved imaging quality/. We present laboratory data of before and after results showing enhanced 3D imaging resulting from precise laser frequency control.

In order to optically reconstruct the three-dimensional (3-D) surface shape of moving objects or deformation processes, aside from high-speed cameras, high-speed projectors and/or short projection sequences are necessary. One approach is to project a series of aperiodic sinusoidal fringes, e.g., by using an array projector that can achieve frame rates of several 10 kHz. So far, we have demonstrated the fundamental functionality of a 3-D sensor based on this projection technique. Now the measurement principle itself is to be compared with phase-shifting fringe projection as probably the most widely used technique. Theoretical considerations as well as experimental investigations are conducted to derive criteria for the design of optimal sequences of aperiodic sinusoidal fringes and to compare the number of patterns of both approaches necessary for comparable accuracies.

The speckle interferometry is a useful optical deformation measurement method in the object with rough surfaces. The deformation measurement method by using only two speckle pattern has also been proposed in ESPI by using Fourier transform. Then, the method can measure the deformation in high resolution. Furthermore, the method can measure not only the out-of-plane but also the in-plane deformation measurement of the objects with rough surfaces in high resolution. Then, the methods can also measure three-dimensional deformation. Many kinds of the three-dimensional measurement methods based on the speckle interferometry have been proposed. However, the parameters in sensitivity matrices of these conventional methods are not generally same concerning the three directions. The method of which sensitivity in three directions is not same cannot be employed as the exact three-dimensional measurement method. In this paper, the method of which sensitivity in three directions is same is proposed. The optical system is set up under the concept of the proposed method. The multi-recording technology of the signals of the deformations for speckle interferometry using one camera is discussed. From the experimental results, the validity of the novel method is confirmed.

3D microscopes based on white light interference (WLI) provide precise measurement for the topography of engineering surfaces. However, the display of an object in its true colors as observed under white illumination is often desired; this traditionally has presented a challenge for WLI-based microscopes. Such 3D color display is appealing to the eye and great for presentations, and also provides fast evaluation of certain characteristics like defects, delamination, or deposition of different materials. Determination of color as observed by interferometric objectives is not straightforward; we will present how color imaging capabilities similar to an ordinary microscope can be obtained in interference microscopes based on WLI and we will give measurement and imaging examples of a few industrial samples.

This work reports on the development of a binary pseudo-random test sample optimized to calibrate the MTF of optical microscopes. The sample consists of a number of 1-D and 2-D patterns, with different minimum sizes of spatial artifacts from 300 nm to 2 microns. We describe the mathematical background, fabrication process, data acquisition and analysis procedure to return spatial frequency based instrument calibration. We show that the developed samples satisfy the characteristics of a test standard: functionality, ease of specification and fabrication, reproducibility, and low sensitivity to manufacturing error.

In recent years, optical coherence tomography (OCT) became gained importance in medical disciplines like ophthalmology, due to its noninvasive optical imaging technique with micrometer resolution and short measurement time. It enables e. g. the measurement and visualization of the depth structure of the retina. In other medical disciplines like dermatology, histopathological analysis is still the gold standard for skin cancer diagnosis. The EU-funded project VIAMOS (Vertically Integrated Array-type Mirau-based OCT System) proposes a new type of OCT system combined with micro-technologies to provide a hand-held, low-cost and miniaturized OCT system. The concept is a combination of full-field and full-range swept-source OCT (SS-OCT) detection in a multi-channel sensor based on a micro-optical Mirau-interferometer array, which is fabricated by means of wafer fabrication. This paper presents the study of an experimental proof-of-concept OCT system as a one-channel sensor with bulk optics. This sensor is a Linnik-interferometer type with similar optical parameters as the Mirau-interferometer array. A commercial wavelength tunable light source with a center wavelength at 845nm and 50nm spectral bandwidth is used with a camera for parallel OCT A-Scan detection. In addition, the reference microscope objective lens of the Linnik-interferometer is mounted on a piezo-actuated phase-shifter. Phase-shifting interferometry (PSI) techniques are applied for resolving the conjugate complex artifact and consequently contribute to an increase of image quality and depth range. A suppression ratio of the complex conjugate term of 36 dB is shown and a system sensitivity greater than 96 dB could be measured.

Since its invention in the 19th century, schlieren imaging has been an essential method for studying many aerodynamic effects, particularly convection and shock waves, but the classical method using parabolic mirrors is extremely difficult to set up and very expensive for large fields of view. Focusing schlieren methods have made large- area schlieren more feasible but have tended to be difficult to align and set up, limiting their utility in many applications We recently developed an alternative approach which utilizes recent advances in digital display technology to produce simpler schlieren system that yields similar sensitivity with greater flexibility.

A digital speckle based stereo microscope strain measurement system is developed to investigate the forming limit diagram (FLD) of miniature sheet metal under hydraulic bulge testing conditions. A stochastic speckle pattern is sprayed on the surface of the tested metal before forming. A series of images are recorded by two cameras mounted on a binocular stereo microscope during the hydroforming process. The critical major and minor strains are then calculated and plotted to construct the forming limit curve. The key technologies applied in the system are discussed in detail, including stereo microscope calibration and large deformation strain filed determination. First, considering complex optical paths and high magnification of the stereo microscope, an accurate combined distortion correction model is proposed to optimize the intrinsic and extrinsic parameters of the stereo microscope. Then, to solve the problem of strain measurement of the tested metal in large deformation situation, a large deformation measurement scheme based on deformation continuity of adjacent images is proposed. And an algorithm of limit strain determination based on spline model is proposed to calculate the critical strains at the onset of plastic instability. Finally, with our self-developed stereo microscope imaging system and sheet metal hydraulic bulging setup, FLD determination tests are conducted to validate the performance of the system. And the measured FLD is compared with the simulation results that predicted by the finite element method. The simulation and experimental results confirm that the proposed system is feasible to measure the full-field strain during the whole bulging processes and provides a better solution for forming limit diagram prediction.

Modern digital recording and processing techniques combined with new lighting methods and relatively old schlieren visualization methods move flow visualization to a new level, enabling a wide range of new applications and a possible revolution in the visualization of very large flow fields. This paper traces the evolution of schlieren imaging from Robert Hooke, who, in 1665, employed candles and lenses, to modern digital background oriented schlieren (BOS) systems, wherein image processing by computer replaces pure optical image processing. New possibilities and potential applications that could benefit from such a capability are examined. Example applications include viewing the flow field around full sized aircraft, large equipment and vehicles, monitoring explosions on bomb ranges, cooling systems, large structures and even buildings. Objectives of studies include aerodynamics, aero optics, heat transfer, and aero thermal measurements. Relevant digital cameras, light sources, and implementation methods are discussed.

Experience at the Laboratory for Laser Energetics has shown that broadband base vibrations make it difficult to position cryogenic inertial confinement fusion targets. These effects must be mitigated for National Ignition Facility–scale targets; to this end an active vibration stabilization system is proposed. A single-mode optical fiber strain probe and a novel fiber contained heterodyne interferometer have been developed as a position feedback sensor for the vibration control system. A resolution limit of 54.5 nƐ; is measured with the optical strain gauge, limited by the lock-in amplifier. Experimental measurements of the sensor that show good agreement with reference resistive strain gauge measurements are presented.

We present a numerical method for retrieving the refractive index distribution in two-dimensional gradient-index media from external measurements of laser beam deflection. Using an iterative approach to ascertain the boundary positions and angles of probe beams that transit the optical medium and constructing approximate beam trajectories that satisfy these boundary values, we show that the inverse problem can be reduced to the inversion of a sparse linear algebraic system. The beam trajectories are subsequently corrected using an iterative ray trace procedure that continually refines the computed solution and the associated boundary values. We demonstrate our method in simulation by calculating the refractive index distribution of a hypothetical 2-D gradient-index element from computer-generated external beam deflection data, where RMS index errors below 1% of the index range (n_max − n_min) are achieved.

Currently large volume, high accuracy three-dimensional (3D) metrology is dominated by laser trackers, which typically utilize a laser scanner and cooperative reflector to estimate points on a given surface. The dependency upon the placement of cooperative targets dramatically inhibits the speed at which metrology can be conducted. To increase speed, laser scanners or structured illumination systems can be used directly on the surface of interest. Both approaches are restricted in their axial and lateral resolution at longer stand-off distances due to the diffraction limit of the optics used. Holographic aperture ladar (HAL) and synthetic aperture ladar (SAL) can enhance the lateral resolution of an imaging system by synthesizing much larger apertures by digitally combining measurements from multiple smaller apertures. Both of these approaches only produce two-dimensional imagery and are therefore not suitable for large volume 3D metrology. We combined the SAL and HAL approaches to create a swept frequency digital holographic 3D imaging system that provides rapid measurement speed for surface coverage with unprecedented axial and lateral resolution at longer standoff ranges. The technique yields a “data cube” of Fourier domain data, which can be processed with a 3D Fourier transform to reveal a 3D estimate of the surface. In this paper, we provide the theoretical background for the technique and show experimental results based on an ultra-wideband frequency modulated continuous wave (FMCW) chirped heterodyne ranging system showing ~100 micron lateral and axial precisions at >2 m standoff distances.

The last place an optics manufacturer wants to physically touch a lens is at the center. However, this is precisely what is currently done to measure center thickness of lenses. Using contact methods, the question is not whether the optic is damaged, it is whether the resulting damage is acceptably low. At Bridger Photonics, we have proven the feasibility of a non-contact center thickness metrology system to address this need. The apparatus uses a technique similar to swept-frequency optical coherence tomography to measure both physical thickness and optical thickness. From these measurements, the group index of refraction can also be determined. Moreover, the phase index can be determined, given the Sellmeier coefficients. In this presentation, we will report our demonstrated measurement range of 75 mm optical thickness (larger possible), as low as 20 nm precision, and group index of refraction determined to better than 5 parts is 10⁵. We believe the metrology system resulting from these proof-of-principle demonstrations will be a valuable tool for precision optics manufacturing.

Extrinsic calibration accuracy for time-of-flight (ToF) cameras is affected by accumulated errors which are generated by recognition of conventional objects with multi-characteristics such as checkerboard. In order to eliminate accumulated errors, in this paper, we propose a novel extrinsic calibration method of ToF cameras with a virtual multi-cubes shaped object. First, we establish the model of a 3-axis translation stage composed of three linear translation stages which are orthogonal to each other. Then, a virtual multi-cubes shaped object with multi-characteristics is generated from an optimized combination of multi-motions of the 3-axis translation stage. After recognizing corner characteristics of this multi-cubes shaped object, the proposed method is accomplished by performing the least square method. Our experimental results show that the measurement accuracy of ToF camera is improved from ±10mm to 6.85mm, which is much better than that of the conventional method based on a 2D plane checkerboard. The proposed method has the ability to improve calibration accuracy to a high level. It may find great potential applications in many fields.

Despite significant technological advances in the field of fiber optic communications, one area remains surprisingly ‘low-tech’: fiber termination. In many instances it involves manual labor and subjective visual inspection. At the same time, high quality fiber connections are one of the most critical parameters in constructing an efficient communication link. The shape and finish of the fiber end faces determines the efficiency of a connection comprised of coupled fiber end faces. The importance of fiber end face quality becomes even more critical for fiber connection arrays and for in the field applications. In this article we propose and demonstrate a quantitative inspection method for the fiber connectors using reflected wavefront technology. The manufactured and polished fiber tip is illuminated by a collimated light from a microscope objective. The reflected light is collected by the objective and is directed to a Shack-Hartmann wavefront sensor. A set of lenses is used to create the image of the fiber tip on the surface of the sensor. The wavefront is analyzed by the sensor, and the measured parameters are used to obtain surface properties of the fiber tip, and estimate connection loss. For example, defocus components in the reflected light indicate the presence of bow in the fiber end face. This inspection method provides a contact-free approach for quantitative inspection of fiber end faces and for estimating the connection loss, and can potentially be integrated into a feedback system for automated inspection and polishing of fiber tips and fiber tip arrays.

Semiconductor laser range-finder systems use so-called “time-of-flight” methods that require us to modulate semiconductor lasers’ intensity and frequency, and detect those of reflected lights, in order to compare optical paths to the reference and the target. But, accurate measurement requires both high-speed modulation and detection systems. By taking advantage of semiconductor lasers’ broad- spectrum frequency noise, which has a range of up to a few GHz, and converting it to intensity noise, we were able to generate a set of high-speed physical random numbers that we used to precisely measure the distance. We tuned the semiconductor lasers’ oscillation frequencies loosely to the Rb absorption line and converted their frequency noise to intensity noise, in the light transmitted. Observed through a frequency discriminator, beams traveling along two different paths will always share intensity noise patterns, but there is a time lag. We calculate the cross-correlation of the two signals by sweeping their time lags. The one with the highest degree of correlation was that corresponding to the difference in the length of the two optical paths. Through our experiments, we confirmed that the system was accurate up to a distance of 50 m, at a resolution of 0.03 m, when the sampling rate was adjusted to 0.2 ns.

This paper proposes a rapid body scanning system that uses optical digital fringe projection method. Twelve cameras and four digital projectors are placed around the human body from four different directions, so that the body surface threedimensional( 3D) point cloud data can be scanned in 5~8 seconds. It can overcome many difficulties in a traditional measurement method, such as laser scanning causes damage to human eye and low splicing accuracy using structured white light scanning system. First, an accurate calibration method based on close-range photogrammetry, is proposed and verified for calibrating the twelve cameras and the four digital projectors simultaneously, where a 1m×2m plate as calibration target with feature points pasted on its two-sides is used. An experiment indicates that the proposed calibration method, with a re-projection error less than 0.05pixels, has a considerable accuracy. The whole 3D body surface color point cloud data can be measured without splice different views of point cloud, because of the high accuracy calibration results. Then, in order to measure the whole body point cloud data with high accuracy, a combination of single and stereo camera measuring method, based on digital fringe projection, has presented to calculating 3D point cloud data. At last, a novel body chromoscan system is developed and a human body 3D digital model was scanned, by which a physical body model was manufactured using 3D printing technology.

In this paper we present the novel design and proof of concept of an active holographic camera consisting of two array detectors and Liquid Crystal on Silicon (LCOS) Spatial Light Modulator (SLM). The device allows sequential or simultaneous capture of two Fresnel holograms of 3D object/scene. The two detectors configuration provides an increased viewing angle of the camera, allows to capture two double exposure holograms with different sensitivity vectors and even facilitate capturing a synthetic aperture hologram for static objects. The LCOS SLM, located in a reference arm, serves as an active element, which enables phase shifting and proper pointing of reference beams towards both detectors in the configuration which allows miniaturization of the camera. The laboratory model of the camera has been tested for different modes of work namely for capture and reconstruction of 3D scene and for double exposure holographic interferometry applied for an engineering object under load. The future extension of the camera functionalities for Fourier holograms capture is discussed.

Because of its compact size and portability, optical fiber has been wildly used as optical paths in frequency-scanning interferometers for high-precision absolute distance measurements. However, since the fiber is sensitive to ambient temperature, its length and refractive index change with temperature, resulting in an optical path length drift that influences the repeatability of measurements. To improve the thermal stability of the measurement system, a novel frequency-scanning interferometer composed of two Michelson-type interferometers sharing a common fiber optical path is proposed. One interferometer defined as origin interferometer is used to monitor the drift of the measurement origin due to the optical path length drift of the optical fiber under on-site environment. The other interferometer defined as measurement interferometer is used to measure the distance to the target. Because the optical path length drift of the fiber appears in both interferometers, its influence can be eliminated by subtracting the optical path difference of the origin interferometer from the optical path difference of the measurement interferometer. A prototype interferometer was developed in our research, and experimental results demonstrate its robustness and stability. Under on-site environment, an accuracy about 4 μm was achieved for a distance of about 1 m.